BfX

BfX is based on the book
of Arthur
Pejsa. Pejsa deploys the Siacci
method for approximating bullet trajectories. Here one takes a
flat-fire approximation for trajectories. That makes the math easier,
but limits the elevations to a maximum of 15 degrees. Beyond this angle
the approximation becomes too inaccurate for some use-cases. Another
characteristic of the Siacci method is the parametrization of the drag
function by (a few) splines allowing closed form mathematical
trajectory calculations. For a discussion on
ballistics see the link page and Wikipedia's page on exterior
ballistics in English
or Dutch.
The algorithms that are deployed are derived by myself, following
Pejsa's approach. As a consequence some of the typos are not affecting
BfX, the formulas have metric constants, some approximations are
skipped, the range of applicability extends below the speed of sound
and BfX supports many drag
functions. The math was done partly with Mathematica,
a computer program
with which one can manipulate equations.